Ophthalmic glass



Patented Sept. 26, 1950 UNITED STATES PATENT OFFICE OPHTHALMIC GLASSWilliam H. Armistead, Corning, .N. Y., assignor to Corning Glass Works,Corning, N. Y., a corporation of New York No Drawing. ApplicationNovember 22, 1948, Serial No. 61,527

and a softening point of about 725 C. Softening point is thattemperature at which a fibre of the glass of specified size willelongate under its own weight at a given rate when suspended through asmall furnace of specified dimensions (Viscosity of Glass Between theStrain Point and Melting Temperature, by H. R. Lillie, Jour.

Am. Cer. Soc., vol. 14, page 502, July 1931). They must have gooddevitrification resistance during sealing and adequate chemicaldurability or resistance to weathering. Their purpose requires an indexof refraction for the D line (nD) between 1.57 and 1.70 and it isdesirable that they have a dispersive index (11) which is as high aspossible. Prior ophthalmic glasses of high refractive index haveamaximum dispersive index of about 32 which is less than desired. Theprior glasses of lower refractive index have a maximum dispersive indexof about 50 but have insufficient chemical durability.

The primary object of this invention is to provide ophthalmic glasseswhich have higher dis.- persive indices than have hitherto beenobtainable in glasses of this type without sacrifice of other desirableproperties.

Another object is to provide ophthalmic glasses having opticalproperties ranging from nD=1.70, preferably 1LD=1.65, 11:46, to nD=1.57,preferably nD=l.59, 11:53, but having at the same time good chemicaldurability, softening points below 700 C. and thermal expansioncoefficients between 83 and 95 l0-" cm. per cm. per degree C. y

In general, I have found that the above objects may be attained withglasses comprising 33% to 60% SiOz, 1% to 7% B203, 2% to 15% ZrOz, to28% BaO, .3% to 5% L120, 1% to 15% NazO, 0% to 18% PhD, and containingZnO and CaQtotaling together at least 3% but individu- 7 Claims. (Cl.106-53) ally amounting to less than 3%, the glasses containing at leastthree bivalent metal oxides, the total percentage of such bivalent metaloxides being between and 50%. In lieu of Na2O,-

K may be substituted wholly or in part.

For the present purpose the outstanding fault of prior glasses is theirhigh dispersion for light of different wave lengths, that is, their lowdispersive index, which causes excessive color aberration,

Although it may be absent, the present glasses preferably should containat least 5% BaO, because BaO raises the refractive index without undulylowering the dispersive index. Morethan 28% BaO may causedevitrification. The ,useof 132.0 in substantial amounts tends toraiseithef liquidus temperature of the glass objectionably, but thepresence of CaOand ZnO or PbO counteracts this. The presence of PbO isdesirable also,

because it raises the refractive index and helps to. s-often'the glass.Since PbO tends to lower the dispersive index excessively, not more thanabout 18% thereof should be used.

CdO and S10 also raise the refractive index.-

They are particularly valuable for further increasing the refractiveindex without causing devitrification in glasses having large BaOcontents. Up to 15% of each may thus be employed.

Other oxides, if desired, may be added with benefit as follows: up to8%, but preferably not over 5%, A1203 may be added, preferably but not.necessarily in lieu of SiOz. Such addition increases the resistance ofthe glass to devitrification.

TiOz may be incorporated in the glass with advantage to the opticalproperties and chemical durability. Both T102 and ZrOz tend to raise therefractive index of the glass more than the other constituents but,whereas Z1'O2 has only a slight effect on the dispersive index, T102 hasa strong depressing effect on it. Hence I prefer to use as much ZIOz,between 2% and 15%, as will dissolve in the glass and to add as muchT102 as possible without unduly lowering the dispersive index. thus beadded.

The expansion coeflicient for suitable sealingv to the standard opticalcrown glass will vary somewhat with softening point and withcomposition, and the new glasses will seal satisfactorily if theirexpansion coefficients are between Up to about 10% TiOz may 83 l0-' and95 10 cm. per cm. per degree C.

The following compositions in weight percentage as calculated from theirbatches are given by way of example but not as limitations of theinvention:

l n n Softening point, C Exp; Coefi. x 10 c,

It is characteristic of the new glasses that they contain a substantialamount of 2102. Commercial ZrO2 sometimes contains a small amount ofuranium as an impuritywhichis sufficient to cause fluorescence in brightlight This sometimes creates the appearance of an objec-l' tionable fogor haziness before' the eyes when spectacle lenses composed of suchglasses are worn in strong light. I have found that the objectionablefluorescence can be prevented bymelting the glass under reducingconditions or by theaddition of a small amount of SnO2. The latterdecomposes sufficiently during melting to cause reduction of the uraniumto a lower valence which does not fiuoresce;

, I claim: I I V 1. An ophthalmic glass which comprises 33%above-indicated proportion, the total percentage of bivalent metaloxides being 15% and 50%, the softening point being below 700 C., therefractive index (nD) being between 1.57 and 1.70, and

the thermal expansionooefiicient being between 83 10 and 95 l0 'cm. percm. per C. between and 300 C. V

2. An ophthalmic glass whichcomprises 33% t0 60%8102, 1% t0 7% B203, 2%13.0 15% ZrOa 0.3% to H20, 1% to of an alkali metal oxide selected fromthe group'consisting'of NazO,

K20, and mixtures of NazO and K20, and at least three bivalent metaloxides in the indicated proportions selected from'the group consistingof-up to 18% P100, 5% to 28% BaO, up to 15% CdO, upto 15% Sr(), and atleast 3% of a mixture of ZnO' and CaO, the maximum proportion of eitherZnO or CaO in said mixture being less than'3%, the selected bivalentmetal oxides including BaO and the mixture of ZnO-and- CaO in theaboveindicated proportions, the total percentage of bi-" valent metaloxides being between 15% and the softening point beingbelow 700 C.,--there; fractive index (nDi'being-between1.57 and1.70,-'

and the thermal expansion coeflicient being Toetween 83x10-' and x10-cm. per cm. per C. between 0 and 300 C.

3.'An ophthalmic glass which comprises 33% to 60% SiO2,'1% to 7% 13203,2% to 15% ZrO2, up to 8% A1203, 0.3% to 5% Li2O, 1% to 15% of an alkalimetal oxide selected from the group consisting of NazO, K20 and mixturesof Na2O and K20, and at least three bivalent metal oxides in theindicated proportions selected from the group consisting of up to 18%PbO, up to 28% BaO, up to'15% CdO, upto 15% SrO, and at least 3% of amixture of ZnO and CaO, the maximum proportion of either ZnO or CaO insaid mixture being less than 3%, the selected bivalent metal oxidesincluding the mixture of ZnO and CaO in the above-indicated proportion,the total percentage of bivalent metal oxides being between 15% and.50%,the softening point being below 700 (3., the refractive index (nD beingbetween 1.57 and 1.70, and. the thermal expansion coeflicient beingbetween 83x10- and 95x10- cm. per cm. per C. between 0and 300 C.

1. An ophthalmic glass which comprises 33% to 65% $102, 1% t0 7%13203,2% 6 315% ZrOa, up to, 10% TiO-2, 0.3% to 5% L120, 1% to 15% of analkali metal oxide selected from the group consisting of Na2O, K20 andmixtures of Na2O and K20, and at least three bivalent metal oxides inthe indicated. proportions selected from the group consisting of up to18% PbO, up to 28% BaO, up to 15% CdO, up to 15% SrO', and at least 3%of a mixture of ZnO and CaO, the maximum proportion of either ZnO or CaOin said mixture being less than 3%, the selected bivalent metal oxidesincluding the mixture of ZnO and Cat) in the above-indicated proportion,the 'total percentage of bivalent metal oxides being between 15% and50%, the softening point being below 700 0., the refractive index (*nD)being between 1.57 and 1.70, and the thermal expansion coefficient beingbetween 83X 10' and 95 10? cm. per cm. per C. between 0 and 300 C;

5. 1111 ophthalmic glass which comprises 33%,

to 60% SiQ2, l% t0 7% B203, 2% to 15% ZlOz, up to 8% A1202, up to 10%T102, 0.3% to 5% L120, 1% to 15 of an alkali metal oxideselected fromthe group consisting of Na2O-, K20 and mixtures of Na2O and K20, and atleast three bivalent metal oxides in the indicated proportions selectedfrom the group consisting of up to 18% B, up to 28% BaO, up to 15% CdO,up to 15 SrO, and at least 3% of a mixture of ZnO and CaO, the maximumproportion of either ZnO or CaO in said mixture being less than 3%,theselected bivalent metal oxides including the mixture of ZnO and CaOin the above-indicated porportion, the total percentage of bivalentmetal oxides being between 15% and 50%, the softening point being below700C the refrac tive index (nD) being between 1.57 and 1.70, and thethermal expansion coefficient being between 83x10 and 95x10 cm. per cm.per C. between 0 and 300 C. I

6. An ophthalmic glass which comprises 33% to 60% Si02, 1% to 7% B203,2% to 15% ZrO2, up to 10% T102, 0.3% to 5% LiO2, 1% to 15% of an alkalimetal oxide selected from the group consisting of NaO2', K20 andmixtures of NA2O and K20, and at least three bivalent metal oxides inthe indicated proportions selected from the group consisting of up of18% PbO, 5% to 28% BaO, up

' to 15% CdO,-up to 15% SnO, andat least3% of a mixture of ZnO and-GaO,the-maximumproportion of either ZnO or CaO in said mixture being lessthan 3%, the selected bivalent metal oxides including BaO and themixture of ZnO and C20 in the above-indicated proportions, the totalpercentage of bivalent metal oxides being between 15% and 50%, thesoftening point being below 700 0., the refractive index (nD) beingbetween 1.57 and 1.70, and the thermal expansion coefficient beingbetween 83 l0- and 95x10 cm. per cm. per C. between 0 and 300 C.

'7. An ophthalmic glass which comprises 33% to 60% S102, 1% to 7% B203,2% to 15% Zr02, up to TiO2, 0.3% to 5% LizO, 1% to of an alkali metaloxide selected from the group consisting of NazO, K and mixtures ofNazO- and K20, and at least four bivalent metal oxides in the indicatedproportions selected from the group con- 6 sisting of up to 18% PbO, 5%to 28% Eat), up to 15% CdO, up to 15% SnO, and at least 3% of a mixtureof ZnO and CaO, the maximum proportion of either ZnO or CaO in saidmixture being less than 3%, the selected bivalent metal oxides includingPbO, BaO and the mixture of ZnO and CaO in the above-indicatedproportions, the total percentage of bivalent metal oxides being between15% and the softening point being below 700 C., the refractive index(nD) being between 1.57 and 1.70, and the thermal expansion coefficientbeing between 83 X 10 and 10 cm. per cm. per C. between 0 and 300 C.

WILLIAM H. ARMISTEAD.

No references cited.

Certificate of Correction Patent No. 2,523,266 September 26, 1950WILLIAM H. ARMISTEAD It is hereby certified that error appears in theprinted specification of the above numbered patent requiring correctionas follows:

Column 3, line 53, after the word being insert between; column 4, line53, for BbO read P110; line 68, for LiO, read M 0; line 70, for N302read Na 0; line 74, and column 6, line 2, respectively, for SnO readSrO; and that the said Letters Patent should be read as corrected above,so that the same may conform to the record of the case in the PatentOflice.

Signed and sealed this 20th day of February, A. D. 1951.

THOMAS F. MURPHY,

Assistant Oommz'ssz'oner of Patents.

1. AN OPHTHALMIC GLASS WHICH COMPRISES 33% TO 60% SIO2, 1% TO 7% B2O3,2% TO 15% ZRO2 0.3% TO 5% LI2O, 1% TO 15% OF AN ALKALI METAL OXIDESELECTED FROM THE GROUP CONSISTING OF NA2O, K2O, AND MIXTURES OF NA2OAND K2O, AND AT LEAST THREE BIVALENT METAL OXIDES IN THE INDICATEDPROPORTIONS SELECTION FROM THE GROUP CONSISTING OF UP TO 18% PBO, UP TO28% BAO, UP TO 15% CDO, UP TO 15% SRO, AND AT LEAST 3% OF A MIXTURE OFZNO AND CAO, THE MAXIMUM PROPORTION OF EITHER ZNO OR CAO IN SAID MIXTUREBEING LESS THAN 3%, THE SELECTED BIVALENT METAL OXIDES INCLUDING THEMIXTURE OF ZNO AND CAO IN THE ABOVE-INDICATED PROPORTATION, THE TOTALPERCENTAGE OF BIVALENT METAL OXIDES BEING 15% AND 50%, THE SOFTENINGPOINT BEING BELOW 700*C., THE REFRACTIVE INDEX (ND) BEING BETWEEN 1.57AND 1.70, AND THE THERMAL EXPANSION COEFFICIENT BEING BETWEEN 83X10**-7AND 95X10**-7 CM. PER CM. PER *C. BETWEEN 0* AND 300*C.